Tone quality control



Feb. 20, 1934.

H. J. LOFTIS TONE QUALITY CONTROL Filed Feb. 14, 1930 2 Sheets-Sheet l mkr Feb- 20, 1934. H. J. LOF-ns TONE QUALITY CONTROL Filed Feb. 14, 1930 2 Sheets-Sheet 2 f/LAMf/vr supp; Y

Patented Feb. 20, 1934 UNITED STATES PATENT oi-I-iciazl 1,947,557 TONE QUALITY CONTROL Delaware Application February 14, 1930. Serial No. 428,374

'5 Claims. (01.250-16) This invention relates to a tone quality control and in particular to an adjusting device accessible from the exterior or" the cabinet.

An object of this invention is to provide adjusting means for setting the tone quality output of a radio signaling device or the like and to provide a visual indicator that indicates the relative position to which the tone quality control has been set. This has been accomplished by providing means associated with the panel of a radio receiver, or the like, said means being connected to an adjustable element in the tone quality control and by providing a visual indicator associated with said first mentioned means that indicates the tone quality or fidelity of said receiver.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred embodiment of one form of the present invention is clearly shown.

In the drawings:

Fig. l shows a front elevation of a conventional radio cabinet having the base broken away.

Fig. 2 shows a fragmentary plan View of a radio receiver; being provided with a tone quality control.

Fig. 3 is a front elevation of the tone quality control with part of the panel broken away.

Fig. 4 discloses a schematic wiring diagram showing the tone quality control as applied to a push-pull audio frequency amplifier.

It is very difficult to get substantially a fiat amplification characteristic of the output of the audio frequency amplifiers in a radio receiver. This distortion may be due to numerous causes such as the loud speaker, the transformer characteristics, over-loading one or more of the tubes, etc. When the ratio of the amplitude of the low audio frequency signals to the amplitude of the high audio frequency signals is not unity the signal currents having the greater amplitude may be decreased by providing a by-pass circuit or a filter that permits part of these currents to be diverted either to ground or to some other suitable circuit. Instead of providing a by-pass circuit, suitable impedance units may be inserted in series with the circuit so that the impedance is not the same for all frequencies as is well known to those skilled in the art.

Where a push-pull amplifier is used a bypass circuit may consist of an impedance shunting the grids of the tubes in the push-pull ampliiier. This impedance may consist of a condenser or an. inductance or both used with.V or without a resistance element. If every receiver were identical when finished and if the demands of the users of the radio receiver were identical a xed impedance could be used. However, this is not'the case. For this reason it is advantageous to use an impedance that may be varied so as to adjust the particular radio receiver to its demands. V

The electrical circuit of` the tone quality control in the preferred embodiment as disclosed in Fig. 4 consists of a condenser 18 connected in series with a variable resistance 20 that may be changed by moving the contact 22. In this particular modification the condenser 18 and the resistance 20 connect the grids 10 and 12 of the tubes 14 and 16, respectively, of a push-pull audio frequency amplifier. As the condenser 18 offers less impedance to the high frequency currents than to low frequency currents it can be readily seen that some of the input high frequency currents in the transformer winding 24 will be shunted through the condenser 18 and the resistance 20. The amplitude of the high frequency currents that are shunted may be varied by adjusting the resistance 20 from zero to the maximum resistance. A resistance having a resistance of one megohm hasbeen found to give very satisfactory resultsin some types' of radio receivers. Although a push-pull audio frequency amplifier has been shown, the tone quality control may be applied to other stages of amplification as is well understood by those skilled in the art. f

'I'he mechanical structure for varying theresistance 20 is disclosed in Figs. 1, 2 and 3 where the reference characterV 30 indicates a radio receiver cabinet provided with a. panel 32 which may be enclosed by a pair of doors 34 and 36 hinged vto the cabinet or attached thereto in any suitable manner. The panel 32 is provided with an aperture 38 which provides a window for 'the indicator 40. The panel also carries a plurality of ooi knobs 42, 44 and 4a that are used for adjusting ,g

In order to indicate the relative position of H0 the contact 22 with respect to the resistance 20 'its ser

a visual indicator has been provided which includes a traveling pointer or indicator 52 slidably mounted on a rod 54 and actuated by a exible belt 56 passing over the pulley 50 keyed to the shaft 48 by a set screw 59 and over an idler 60 carried on a shaft 62. The tension of the belt 56 is kept constant by means of a spring 64 interposed therein. The indicator 52 is attached to the belt 56 by a pair of screws 58. Although a belt has been disclosed in this embodiment, any flexible cord may be used to actuate the indicator 52 or a rack and pinion. The indicator 52 which is mounted back of the panel, as clearly `seen in Fig. 2, may be seen through a translucent window 66 mounted in the panel 32 in any suitable manner. The tone quality of the output may be indicated on the translucent window 66. Instead of a traveling pointer carried by the flexible belt56, a scale may be carried by this belt which coop, crates with a fixed pointer to indicate the relative position of the contact 22 with the resistance 20.

The rod 54 may be attached to the radio chassis 68 by a pair of brackets 70 and '72. The function of the rod 54 is to prevent vibration of the pointer 52. This being the case, any other suitable means may be adapted to serve as a guide for the pointer 52. By rotating the knob or handle 42 the contact 22 is actuated along the resistance element 20 and the indicator 52 is actuated along the translucent window 66 carrying suitable insignia to visually indicate the tone quality output.

The purview of this invention is not limited to the particular indicating driving means used, as any indicating or driving means other than the one disclosed may be used.

While the form of embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms mightV be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In combination with a radio receiver provided With a control panel and a variable tone control impedance disposed behind said panel, a tone control knob on the front of the panel, at least two pulleys disposed behind the panel, means for securing the variable' element of said tone control impedance to one of the pulleys, means for aixing said control knob to said one pulley, a belt connecting said pulleys, a scale on said panel adjacent said control knob provided with tone indications corresponding to adjustments of said impedance, a pointer secured to said belt for movement adjacent the scale indications when said control` knob is adjusted to vary said impedance, and means for guiding the movement of said pointer in such a manner as to prevent vibration of the pointer during movement thereof. v Y

2. In combination with a radio receiver provided with a control panel and a variable tone control resistor disposed behind said panel, a tone control knob on the front of the panel, at least two pulleys disposed behind the panel, means for securing the variable element of said tone control resistor to one of the pulleys, means for afxing said control knob to said one pulley, a belt connecting said pulleys, a scale on said panel adjacent said control knob provided with tone indications corresponding to adjustments of said resistor, a guide rod, and a pointer secured to said belt for sliding movement over the rod adjacent the scale indications when said control knob is adjusted to vary said resistor.

3. In combination with a radio receiver provided Witl'i a control panel and a variable tone control impedance disposed behind said panel, a tone control knob on the front of the panel, at least two pulleys disposed behind the panel, means for securing the variable element of said tone control impedance to one of the pulleys, means for afiixing said control knob to said one pulley, a belt connecting said pulleys, a translucent scale on said panel adjacent said control knob provided with tone indications corresponding to adjustments of said impedance, a pointer secured to said belt for movement adjacent the scale indications when said control knob is adjusted to vary said impedance, and means distinct from the belt, knob and scale for guiding the movement of ,said pointer in such a manner as to prevent vibration of the pointer during movement thereof.

4. In combination with a radio receiver provided with a control panel and a Variable tone control impedance disposed behind said panel, a tone control knob on the front of the panel, at least two pulleys disposed behind ther panel, means for securing the variable element of said tone control impedance to one of the pulleys, means forraiiixing said control knob to said one pulley, a belt connecting said pulleys, a scale on said panel adjacent said control knob provided with tone indications corresponding to adjustments of said impedance, a guide rod behind the panel, and a pointer disposed behind the panel and secured to said belt for sliding movement over said rod adjacent the scale indications when said control knob isA adjusted to vary said impedance.

5. In combination with a radio receiver provided with a control kpanel and a variable tone control resistor' disposed behind said panel, a

' adjacent the scale indications when said control knob is adjusted to vary said resistor.

HOMER J. LOFTIS.

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